When a data stream, for example a sequence of images or video, is transmitted over a communication network, some data in the data stream are liable to be lost or corrupted.
The consequence of the data loss or corruption that occurs during the transmission of a video sequence is the appearance of artifacts (or artificial interference) in some images in the video sequence. These artifacts reduce the quality of the video sequence.
In order to improve the image quality, error concealment methods are applied to the images in the image sequence.
The error concealment methods can be divided into temporal methods and spatial methods.
Temporal methods consist of using the data in the previously decoded images in order to estimate the data corresponding to an image part comprising missing or erroneous data.
These methods present satisfactory results when the difference between a current image to be corrected and the previous images is small, that is to say when these images resemble each other.
Spatial methods, for their part, consist of using the correctly decoded data of a current image in order to estimate the data corresponding to a part of the current image comprising missing or erroneous data.
In general, these methods present less satisfactory results than the temporal methods, except when a change in scene takes place between the image to be corrected and the previously decoded image which will be used as a reference. This is because the image following a scene transition may be very different from the previous images. It is thus ineffective to use a previous image for estimating the erroneous image part.
The document US 2007/0189398 describes a method for concealing the errors in an image in a video sequence by means of an error concealment technique selected from temporal and spatial concealment techniques. The selection of the error concealment technique is made using a criterion of similarity between two images.
Nevertheless, the result obtained is not entirely satisfactory, the image comprising corrected data having in fact a difference with respect to the original image. Thus, when an image comprising corrected or concealed data is used as a reference (or as the previous image) in the application of a temporal concealment method, the errors in the image propagate and may increase in the following images.
It is therefore possible for two images that resemble each other to be considered to be different because of the error caused by the error concealment method and for the concealment method selected not to be the ideal method.